In the archery industry, many manufacturers have attempted to simultaneously achieve an arrowhead that has aerodynamic properties similar to those associated with non-bladed arrowheads known as field points or nib points, while also achieving effective cutting areas provided by bladed arrowheads, which are often referred to as broadheads. Broadhead blades which are exposed during flight often result in undesirable steering of the front portion of the arrow, causing the arrow to deviate from a perfect flight path that coincides with a longitudinal axis of the arrow shaft, when loaded or drawn within an archery bow.
By reducing the surface area of a broadhead blade, the undesirable steering effects can be reduced. However, by reducing the surface area of a blade, the cutting area within a target or game is also reduced, resulting in a less effective entrance and exit wound.
Conventional blade-opening arrowheads have been designed so that a substantial portion of the blade is hidden within the body of the arrowhead, such as during flight of the arrow. Upon impact, such blades are designed to open and thereby expose a cutting surface or sharp edge of the blade. When the blades of such conventional arrowheads are closed and substantially hidden within the body, the exposed, surface area is reduced and thus produces relatively less undesirable steering effects.
Many of such conventional blade-opening arrowheads rely upon complex mechanisms, some of which fail to open reliably because of a significant holding or closing force that must be overcome, and others that open prematurely because of structural deficiencies within the blade carrying body that fail upon impact, resulting in non-penetration of the arrow. With such relatively complex mechanisms, dirt or other materials that may enter such conventional arrowheads can affect the reliability of the arrowhead, particularly after prolonged use. Examples of such mechanisms are disclosed in U.S. Pat. Nos. 5,112,063, 4,998,738 and 5,082,292. The deployable cutting blades are connected by pivot features to a plunger. The cutting blades pivot between an open cutting position and a closed non-barbed position. U.S. Pat. No. 5,102,147 discloses a ballistic broadhead assembly that has blades pivotally mounted on an actuating plunger. Upon impact, the actuating plunger thrusts the blades outwardly and forwardly.
Other conventional broadheads which have blades partially hidden within the body use annular retaining rings, such as O-rings, wraps, bands and the like, in order to maintain the blades in a closed position during flight. Upon impact, such annular retaining rings are designed to sheer or roll back along the opening blades, in order to allow the blades to move to an open position. Quite often, such conventional annular retaining rings are prone to cracking, particularly when the elastomer material dries out. Upon release of a bowstring, the rapid acceleration and thus significant opening forces move the blades in an opening direction. The conventional annular retaining rings counteract such opening forces. However, when the ring material dries out, cracks or is otherwise damaged, the blades may open prematurely, resulting in significant danger or injury to the archer.
Many of the annular retaining rings are designed for one use and thus must be replaced after each use. In addition to the cost involved with supplying such consumable item, the annular retaining rings are difficult and time-consuming to install, such as when hunting, particularly during inclement weather. Furthermore, the material properties of such conventional annular retaining rings can be affected by temperature changes, thereby resulting in different bias forces that cause the blade to open prematurely or to not open when desired.
One class of mechanical broadheads deploy the blades in an over-the-top motion, such as disclosed in U.S. Pat. No. 5,090,709. The extendable blades are pivotally connected to a body near the rear of the broadhead body. A ring releasably holds the extendable blades within corresponding slots within the body.
High-speed photography of over-the-top broadheads shows that the blades often do not fully open until after the blades enter the target. Consequently, the full cutting diameter of an over-the-top broadhead is often not available through the depth of the target. Also, as illustrated in FIG. 1, an angled hit with over-the-top broadhead 20 can also result in one of the blades 22A engaging the target 24 before the other blade 22B, potentially applying a deflection force 26 on the broadhead 20. Both the deflection force 26 and blade deployment 22A, 22B during entry of the over-the-top broadhead 20 can dramatically reduce kinetic energy of the arrow.